This invention relates generally to rotary air-to-air transferrers for air conditioning systems and, more particularly, to heat transfer media employed in such heat transferrers.
Rotary air-to-air heat transferrers are well-known in the air conditioning art. They are used in air conditioning systems to remove a portion of the heat from one air stream, such as from the exhaust stream from a heating system, and transfer the same to another air stream, such as the inlet stream to the system. The total energy requirements for heating or cooling buildings are thereby reduced; hence, intitial equipment and operating costs can also be reduced. The primary component of such a heat transferrer is a slowly rotating, open cylinder, commonly called a wheel, through which both incoming and outgoing air streams are passed. This wheel carries an air-permeable material as the heat transfer medium.
One type of heat transfer medium consists of sheets or layers of fibrous, liquid-absorbent material, such as asbestos paper, with alternate sheets or layers being flat or planar and every other layer or sheet being undulating or corrugated. If it is desired to transfer moisture from one stream to the other, the medium typically is impregnated with a desiccant substance such as silica gel or a hygroscopic salt such as lithium chloride.
Examples of this type of heat transfer medium are disclosed in U.S. Pat. Nos. 2,818,934, 3,155,153, 3,307,617 and 3,377,225. U.S. Pat. Nos. 3,176,446 and 3,733,791 disclose other types of substrates for supporting desiccant or hygroscopic materials.
The specific media disclosed in these patents are for the most part quite acceptable for many applications. However, with decreasing availability and rising cost of fuel, there is need for less costly, high efficiency heat transfer medium capable of recovering a higher amount of the thermal energy from an exhaust system.
One of the principal objects of this invention is to provide a relatively inexpensive heat transfer medium for rotary air-to-air heat transferrers employed in air conditioning systems and a method for making same.
Another of the principal objects of this invention is to provide such a heat transfer medium having an improved capability of transferring latent heat.
A further of the principal objects of this invention is to provide a heat transfer medium in which the exposed surfaces of the flow passages are coated with a film of a hygroscopic material in a manner whereby the amount of material available for surface contact by air flowing through the flow passages is maximized.
Other objects, aspects and advantages of the invention will become apparent to those skilled in the art upon reviewing the following detailed description, the drawing and the appended claims.
The heat transfer medium provided by this invention includes alternate flat or planar layers and undulating or corrugated layers of fiber-reinforced, heat-curable, organic, resinous material disposed in parallel relationship. The layers are bonded together at their points of contact to form a self-supporting, water-proof structure including uniformly-spaced, tubular flow channels or passages extending axially from one side to the other in parallel relationship to each other and parallel to the rotational axis of the heat transferrer. The portions of the layers defining the flow passages are substantially non-absorbent relative to water. The surfaces of the flow passages exposed to air flow are coated with a film applied as an aqueous coating solution containing a water-soluble, hygroscopic material for exchanging moisture with air flowing in contact therewith and a sufficient amount of a water-soluble wetting agent to provide a continuous film of the coating solution on the flow passage surfaces.
In a preferred embodiment, the layers are formed from thin sheets of a fibrous material, such as kraft paper, impregnated with at least 50 weight % of a heat-curable organic resin, such as a phenolic or a melamine resin, which is partially cured (B-stage). After corrugating and interleaving, the resultant structure is heated to cure the resin to a hardened state.
The heat transfer medium can be made into wedge-shaped units with the planar and corrugated layers extending either generally radially, through concentric arcs, or through chords relative to the rotational axis of the transferrer.